There's a lot of stuff to keep straight in Watch Dogs, but the way you play the game often comes down to personal preference. Here, I'll walk you through some of the most relevant systems. The game will walk you through the rest, and you can get information about control scheme and such from the main menu.
You can press the appropriate button at nearly any point to bring up the Profiler. While you are profiling, you can see areas of interest around you, including potential hacking targets.
In that mode, you can hack bank accounts or obtain songs or the keys to cars for your collection. Vehicles can be ordered through your phone, when it's convenient, though often it will be easier just to find one parked by the side of the road and drive that.
The Profiler lets you hack into cameras and eliminate threats to Aiden, in a variety of ways that are outlined below.
The Skill Tree determines what Aiden is able to do as he moves through Chicago. It is divided into four segments, with the largest (and most useful) of those being the Hacking segment.
Each skill you gain requires a certain number of skill points. Those skill points are gained as you go up levels by gaining experience. You gain experience points by clearing missions, primarily, but also by doing things like successfully evading police pursuit or performing takedown moves on enemies or shooting them in the head with sniper rifles.
Initially, most of the advanced skills along the tree are locked, even if you have enough points. You'll have to complete the Open Your World mission to gain access to more of them, but that happens relatively early in the campaign.
For reference, you'll likely have around 30 skill points to spend by the time you reach the end of the campaign, even if you're not actively seeking out side challenges. It's easy to have much more besides, if you're taking your time, but don't spend skill points frivolously.
You can bring up the map at any point, even during a mission. If there is a destination where you should be headed, it will show up as a yellow icon. You can click on it and set a waypoint. Then when you start running around the city, you'll have a blue trail to follow that leads you along an optimal route toward that destination. It's a great way to keep yourself on task.
On the map, between missions, it's also possible to fast travel to your hideout. Over the course of the campaign, you will have multiple hideouts available. The icon for your hideouts looks like the Pause button on a DVD player remote. Hideouts let you save your progress and change what time of day it is in a hurry, so they're a useful resource to keep in mind.
Maps also show the various side missions you can complete in your leisure.
Aiden Pearce, the story's protagonist, is a hacker with a criminal past that he's not afraid to use as he tracks down the people responsible for his young niece's death. Hacking can make the game much easier than it would otherwise be, and is often required.
The general plan as you approach a building, particularly a secure facility, should be to look for a camera on a wall or pole. That camera tends to point in the direction of any guards that might provide resistance, and also toward other cameras. You can leapfrog from camera to camera to proceed through a facility. Cameras have limited range, but you'll find them where you need them.
Sometimes, guards carry cameras. As you look down on an area from a camera, you can often see the guards highlighted for your convenience. You can travel to a guard and see things from his chest's perspective as he makes his rounds, which will be necessary to find cameras in some missions.
From security cameras, you can continue to hack and produce a variety of effects. Cameras aren't good only for recon; they also allow you to go on the offensive.
Frequently, missions require you to reach a security panel so that you can reduce the level of protection afforded a building. In some cases, you'll have to physically get within range of a box and press the button indicated. In others, you'll simply need to view one from a distance (usually from within a security camera) and hack it that way. Some of the boxes have an extra layer of security.
Often, the most important boxes cannot be hacked until you have completed a mini-game. This mini-game changes in each case, but plays out in the same general manner. You have to connect blue currents to lock icons. A lock icon will have arrows along anywhere from 1 to 4 sides, all with corresponding wires. When you send juice along all relevant wires, you unlock that icon and can produce a new 'T' or elbow piece that will allow you to direct current to additional locks. When you have unlocked every lock, the mini-game ends (unless there are additional rounds, as there can be closer to the end of the campaign).
Note that some of the mini-games also have a time limit that will be active right from the start, or after you rotate a certain piece. That piece that sets the timer to ticking down is often indicated by a red aura, so it pays to adjust any other elbows and pieces first before you manipulate the one marked as sensitive. If you fail in a hacking attempt, the only penalty is that you have to start over. It doesn't actually compromise Aiden's safety.
As you progress through the game, you'll find crafting components lying all over the place. You can pick these up or purchase them from shops. If you have unlocked the required skills in the Skill Tree, you can then fashion yourself all sorts of useful devices. These include Blackouts, which plunge the surrounding area into blackness during nighttime scenes. That's a terrific way to escape police officers. Grenades are another option. You can build multiple types, including IEDs that can be set in a likely area and then detonated remotely.
Honestly, you shouldn't need most of the crafted items until very near the end of the game, and I had cleared most of the campaign before I bothered learning any of the skills. However, they definitely do make your life easier and you might wish to get your hands on the good stuff earlier, especially if you're having a difficult time.
You'll see a few types of guard over the course of the game, and you can deal with them in a number of ways.
If your guard is a standard opponent, he will fall instantly to a takedown move. Aiden can duck behind crates or similar objects. When the guard approaches and comes within range, a button prompt will appear on-screen. Quickly pressing that button will allow Aiden to perform the takedown move and also net him a boost in experience points. Note that some heavily armored enemies (known as Elite soldiers) can't be taken down in this manner until Aiden has unlocked an advanced ability on the Skill Tree.
Aiden can duck behind cover and shoot at foes, or he can run toward them and press a button to snap onto the nearest target. Neither option is perfect, and it's usually preferable to fire at foes from cover, just because Aiden can't take many hits before he drops.
While shooting, you may be able to slip into Focus mode, if you unlock those abilities from the Skill Tree. This slows down time and you can carefully place your shots. However, it's completely unnecessary and in fact I got through the game without ever devoting points to that discipline. You're better finding a point of cover. Then you can move the cursor around and press a button to move to another point of cover (or around a corner) without ever leaving that protection. As long as you watch your mini-map and don't let anyone flank you, this makes combat a breeze.
If you're at a safe enough distance that you don't have to worry about being seen, you can take out your enemies with hacking abilities. Simply jack into a camera, then scan the area.
Guards may be carrying explosives, in which case you can hack the grenades and often the guards will die in an explosion shortly thereafter. Sometimes, they will manage to toss the grenade away before it can kill them. Note that in either event, the blast will alert other patrolling units to an emergency.
The environment also tends to offer options. You can overload panels on walls or floors to produce explosions that are good at taking out guards, including those wearing armor. Sometimes, you can make a phone ring or a car alarm sound to bring multiple guards close together before you engineer the blast.
It's worth noting here that some guards can also call in for reinforcements. There's an ability in the Skill Tree that can prevent that, though. You can make missions a lot easier if you scout ahead and find and disable any radios that might be used to summon assistance. Why worry about 10 guards when you can keep the number at 5?
Vehicles and Driving
You'll find a variety of vehicles throughout the game. Usually, people are driving them. You can run up to any vehicle and press the button indicated to jump into the car. The driver will be forced out and you can take off down the road. The downside here is that the police may be called to give chase, and they can be a pain in the butt to elude.
Parked cars are another story. You can learn an ability from the Skill Tree that prevents an alarm from sounding. At that point, a parked car is essentially a free ride, and a great way to get from one point to another.
Once you are driving, you can hack as you make your way around the city. This is an important skill. It's possible to hack traffic signals to produce wrecks, or you can hack bridges to make them raise and lower as you see fit. If police are chasing, it's a great way to lose that pursuit. In particular, bridges are good for putting a lot of distance between yourself and the cops, and steam vents are a great way to knock enemy cars out of the running altogether. Just make sure that you don't take out yourself.
If you are driving and you see your car catch on fire and starting to slow, it's a good idea to get out of it quickly. Damaged vehicles can explode, and the blast could take you along with whatever hunk of metal you're trying to coax down the road.
As you roam the city, you'll sometimes find indicators that allow you to accept online contracts, as a fixer. These can be completed to improve your reputation, which unlocks perks as the people of Chicago come to view you more favorably.
I didn't spend a lot of time with online missions, since you only have to complete one of them during the course of the standard campaign, so I will likely revisit this later.